Topic overview

Start with the big picture

UV spectroscopy commonly examines absorption in the 200–400 nm region and identifies transitions such as π→π* and n→π*. A chromophore is the part of a molecule responsible for UV absorption, while auxochromes can alter the absorption wavelength and intensity. Greater conjugation generally shifts absorption to longer wavelengths and can increase intensity. Solvent effects and molar absorptivity help distinguish transition types, while the Beer–Lambert law relates absorbance to concentration. Characteristic aromatic bands and Woodward–Fieser rules provide additional interpretive tools. UV spectroscopy supports analysis of conjugation, impurities, reaction progress, and configuration, but is limited for compounds without significant UV-absorbing chromophores. The lesson also introduces common instrument components.